Abbreviations: PMS, N-methylphenazonium methosulfate; CCCP, carbonylcyanide m-chlorophenylhydrazone; FCCP, carbonylcyanide p-trifluoromethoxyphenylhydrazone; TMPD, N,N,N′,N′-tetramethyl-p-phenylendiamine; DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethylurea